An impression left by the friction ridges of human skin, such as the skin of a human finger, contains information regarding the identity of the human. It is widely known that the appearance of the impression of the human finger, known as a fingerprint, is unique to each human and may be used to confirm the identity of the human. The appearance of the impression of the skin of other human body parts may also be unique to each human and so may also be used to confirm the identity of the human. Such impressions of human skin, when not specific to the skin of the human finger, may be called skin-prints.
In addition to the appearance of the impression left by human skin, the impression may contain chemical species which themselves may be detected in order to obtain further information.
For example, when a human intakes a substance (e.g. by ingestion, inhalation or injection) the substance may be metabolised by the human body giving rise to secondary chemicals known as metabolites. The presence of a particular metabolite can be indicative of a specific intake substance. These metabolites may be present in sweat and, as such, may be left behind in the skin-print, e.g. a skin-print. Detection of such metabolites in a skin-print can be used as a non-invasive method of testing for recent lifestyle activity such as (but not limited to) drug use. Importantly, the taking of a skin-print is much simpler than obtaining other body fluids such as blood, saliva and urine, and is more feasible in a wider range of situations.
Not only this but since the appearance of the skin-print itself provides confirmation of the identity of the person providing the skin-print, there can be greater certainty that the metabolites in the skin-print are associated with the individual. This is because substitution of a skin-print, particularly a fingerprint, is immediately identifiable from appearance whereas substitution of, for example, urine, is not immediately identifiable from appearance. As such, testing for metabolites in a skin-print provides a direct link between the metabolite and the identity of the human providing the skin-print.